Segment Results (Schedule of Net Sales) (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2023	Jun. 30, 2022	Jun. 30, 2023	Jun. 30, 2022
Segment Reporting Information [Line Items]
Total net sales	$ 325.4	$ 321.0	$ 635.6	$ 603.6
Mineral Fiber [Member]
Segment Reporting Information [Line Items]
Total net sales	234.0	234.5	462.4	437.7
Architectural Specialties [Member]
Segment Reporting Information [Line Items]
Total net sales	$ 91.4	$ 86.5	$ 173.2	$ 165.9